Life cycles of European Pteridophytes

Although the need for water for fertilization restricts the distribution of pteridophytes, some are able to persist in remarkably dry situations. Fertility in the sexual cycle may be further limited by several factors, amongst them errors of fertilization, competition between embryos, self-incompatibility, accumulated sporophytic lethals (genetic load) and, in some species, possible physiological interference between the expression of maleness and femaleness in the same gametophyte. Aberrant life-cycles are common in the European ferns. All, so far as known, are dependent on the formation of restitution nuclei, leading to sporangia with 8 spore mother cells. Embryos are formed apogamously. A few life cycles involve apospory and apogamy (and perhaps parthenogenesis), but these are maintained solely in cultivation. Heterosporous cycles are also found in European pteridophytes. In Marsi/ea and Pi/u/aria the formation of viable megaspores involves the regular resorption of three spores in each tetrad, similar to the situation in the seed plants. In Selaginella megasporogenesis is less regular, involving loss ofboth megaspore mother cells and meiotic products. The formation of the megaspores in Isoetes appears to follow simply from the many fewer mother cells in the megasporangium. Both Selaginella and Isoetes seem to represent attempts at heterosporous cycles of limited evolutionary success.Pese a que la necesidad del agua para la fecundación restringe la distribución de los pteridófitos, algunas especies son capaces de vivir en situaciones de notable sequedad. La fecundación en el ciclo sexual puede, por otra parte, estar limitada porotros factores, entre ellos: errores en la fecundación, competenciaentre embriones, autoincompatibilidad, acumulación de factores letales esporofíticos (carga genética), y, en algunas especies, posibles interferencias entre entre laexpresión de la masculinidad y femineidad en el mismo gametófito. Los ciclos vitales aberrantes son frecuentes en los helechos europeos. Todos, por lo que se conoce hasta este momento, dependen de la formación de nucleos de restitución, que dan lugar a esporangios con ocho células madres de las esporas. Los em briones son formados apogám icamente. Unos pocos ciclos vitales presentan aposporia y apogamia (y quizas partenogénesis), pero estos casos únicamente se mantienen en cultivo. Los ciclos heterosporicos también se encuentran en los pteridéfìtos europeos. En Marsi/ea y Pi/u/aria la formación de megásporas viables implica la reabsorción regular de tres esporas en cada tétrada, de forma similar a lo que ocurre en los espermatófitos. En Selaginella la megasporogénesis es menos regular, presentándose la pérdida tanto de las células madre de las esporas y como los productos de la meiosis. La formación de megásporas en Isoetes parece seguir un proceso simple a partir de un número menor de células madres en el esporangio. Tanto Selaginella como Isoetes parecen representar intentos dirigidos hacia ciclos heterospóricos de un éxito evolutivo limitado

The response to high magnetic fields of the vacuum phototriodes for the compact muon solenoid endcap electromagnetic calorimeter

The endcap electromagnetic calorimeter of the Compact Muon Solenoid (CMS) detects particles with the dense fast scintillator lead tungstate (PbWO4). Due to the low light yield of this scintillator photodetectors with internal gain are required. Silicon avalanche photodiodes cannot be used in the endcap region due to the intense neutron flux. Following an extensive R&D programme 26 mm diameter single-stage photomultipliers (vacuum phototriodes) have been chosen as the photodetector in the endcap region. The first 1400 production devices are currently being evaluated following recent tests of a pre-production batch of 500 tubes. Tubes passing our acceptance tests have responses, averaged over the angular acceptance of the endcap calorimeter, corresponding to the range 20 to 55 electrons per MeV deposited in PbWO4. These phototriodes operate, with a typical gain of 10, in magnetic fields up to 4T.PPARC, EC(INTAS-CERN scheme 99-424

Strings, T-duality breaking, and nonlocality without the shortest distance

T-duality of string theory suggests nonlocality manifested as the shortest possible distance. As an alternative, we suggest a nonlocal formulation of string theory that breaks T-duality at the fundamental level and does not require the shortest possible distance. Instead, the string has an objective shape in spacetime at all length scales, but different parts of the string interact in a nonlocal Bohmian manner.Comment: 7 pages, revised, to appear in Eur. Phys. J.

EPR-Bell Nonlocality, Lorentz Invariance, and Bohmian Quantum Theory

We discuss the problem of finding a Lorentz invariant extension of Bohmian mechanics. Due to the nonlocality of the theory there is (for systems of more than one particle) no obvious way to achieve such an extension. We present a model invariant under a certain limit of Lorentz transformations, a limit retaining the characteristic feature of relativity, the non-existence of absolute time resp. simultaneity. The analysis of this model exemplifies an important property of any Bohmian quantum theory: the quantum equilibrium distribution $\rho = |\psi |^2$ cannot simultaneously be realized in all Lorentz frames of reference.Comment: 24 pages, LaTex, 4 figure

Comments on "There is no axiomatic system for the quantum theory"

In a recent paper, Nagata [1] claims to derive inconsistencies from quantum mechanics. In this paper, we show that the inconsistencies do not come from quantum mechanics, but from extra assumptions about the reality of observables

On Modular Homology in the Boolean Algebra, III

AbstractLet F be a field of characteristic p, and if Ω is an n-set let Mn be the vector space over F with basis 2Ω. We continue our investigation of modular homological Sn-representations which arise from the r-step inclusion map. This is the FSn-homomorphism ∂r:Mn→Mn which sends a k-element subset Δ⊆Ω onto the sum of all (k−r)-element subsets of Δ. Using homological methods one can give explicit character and dimension formulae

Boson-fermion unification, superstrings, and Bohmian mechanics

Bosonic and fermionic particle currents can be introduced in a more unified way, with the cost of introducing a preferred spacetime foliation. Such a unified treatment of bosons and fermions naturally emerges from an analogous superstring current, showing that the preferred spacetime foliation appears only at the level of effective field theory, not at the fundamental superstring level. The existence of the preferred spacetime foliation allows an objective definition of particles associated with quantum field theory in curved spacetime. Such an objective definition of particles makes the Bohmian interpretation of particle quantum mechanics more appealing. The superstring current allows a consistent Bohmian interpretation of superstrings themselves, including a Bohmian description of string creation and destruction in terms of string splitting. The Bohmian equations of motion and the corresponding probabilistic predictions are fully relativistic covariant and do not depend on the preferred foliation.Comment: 30 pages, 1 figure, revised, to appear in Found. Phy

Analytic Solutions of The Wheeler-DeWitt Equation in Spherically Symmetric Space-time

We study the quantum theory of the Einstein-Maxwell action with a cosmological term in the spherically symmetric space-time, and explored quantum black hole solutions in Reissner-Nordstrom-de Sitter geometry. We succeeded to obtain analytic solutions to satisfy both the energy and momentum constraints.Comment: LaTeX file, 15 page

Scaling anomaly in cosmic string background

We show that the classical scale symmetry of a particle moving in cosmic string background is broken upon inequivalent quantization of the classical system, leading to anomaly. The consequence of this anomaly is the formation of single bound state in the coupling interval \gamma\in(-1,1). The inequivalent quantization is characterized by a 1-parameter family of self-adjoint extension parameter \omega. It has been conjectured that the formation of loosely bound state in cosmic string background may lead to the so called anomalous scattering cross section for the particles, which is usually seen in molecular physics.Comment: 4 pages,1 figur